New & Noteworthy

Multicellularity a Snap? Maybe so…

February 10, 2012

It took just a few months to go from one cell to many. Image adapted from Ratcliff, et al (PMID: 22307617).

Some people might think that the transition from single-celled creatures to multi-cellular ones must have been tough.  After all, single celled organisms ruled the world for the first one or two billion years of life here on Earth. 

And yet, all multi-celled beasts didn’t evolve from the same ancestor.  Current theories are that multicellularity evolved dozens of times over the ages.  In fact, all of the transitional stages of multicellular life can be seen in the volvocine green algae species around today.  So maybe it isn’t so tricky after all.

Using a very clever screen in yeast, Ratcliff and coworkers have shown that they can get crude multicellular life to evolve in the lab.  Basically they only let the yeast that settled easily to the bottom of a shaking flask go on to reproduce.  Within 60 or so days, they had the beautiful, snowflake-like, multicellular beasts made up of multiple yeast cells shown in the image to the right.

Of course multicellular is more than having a bunch of cells stuck together.  Heck, yeast do that now in something called flocs.  No, to be multicellular, these yeast need to reproduce in a way that generates new multicellular yeast and to have specialized cells.  The snowflake yeast from this experiment did both.

These yeast did not reproduce by creating sperm and eggs that combine to generate progeny.  Instead they reproduced more like a lot of plants do.  They produced smaller versions of themselves which then went on to grow to “adulthood.”  Multicellular life gave birth to more multicellular life.

Cells within these snowflakes were also willing to die for the common good.  For example, the cell where the juvenile snowflake was attached would undergo apoptosis so the juvenile could be released.  No single-celled organism would willingly take that kind of hit for other cells.

So it looks like these researchers managed to evolve multicellular organisms from single-celled ones in just a few months.  Pretty amazing what can be learned from yeast!

Of course some care is needed here.  Yeast actually evolved from a multicellular ancestor so some sort of memory of multicellular life may still be lurking in its genes.  If true, this might make the transition from one to many simpler in yeast than in other single-celled organisms. 

This is why the researchers plan to try similar experiments with single celled organisms that have been single cells throughout their evolutionary life.  Then they’ll have an even better idea about how easy the “one to many cells” transition is.

Multicellular yeast having babies.

by D. Barry Starr, Ph.D., Director of Outreach Activities, Stanford Genetics

Categories: Research Spotlight

Tags: evolution , multicellular , Saccharomyces cerevisiae , yeast